Gobius bratishkoi, Schwarzhans & Klots & Ryabokon & Kovalchuk, 2022

Schwarzhans, Werner, Klots, Oleksandr, Ryabokon, Tamara & Kovalchuk, Oleksandr, 2022, A rare window into a back-reef fish community from the middle Miocene (late Badenian) Medobory Hills barrier reef in western Ukraine, reconstructed mostly by means of otoliths, Swiss Journal of Palaeontology (18) 141 (1), pp. 1-35 : 8-10

Gobius bratishkoi n. sp.

Figure 4a–e

Holotype NMNHU-P PI 2555 , Kozatskyi Yar , western Ukraine, late Badenian, Fig. 4a .

Paratypes 7 otoliths: 5 specimens same data as holotype, NMB P1211 ; 2 specimens, Mlyntsi, NMNHU-P PI 2556 .

Etymology Named after Andriy Bratishko, Tallahassee, Florida (formerly Luhansk, Ukraine), in recognition of his contributions to the fossil fish otoliths of the Eastern Paratethys.

Diagnosis OL:OH = 1.2–1.3. Anterior rim nearly vertical; posterior rim with prominent, rounded postdorsal projection. Dorsal rim with distinct, broad predorsal concavity and narrow postdorsal angle positioned above cauda. Sulcus narrow, relatively short (OL:SuL = 2.1–2.35), inclined at 10–18°. Ostial lobe low; subcaudal iugum small, below anterior part of cauda. Inner face flat; outer face markedly convex.

Description Moderately slender, massive gobiid otoliths reaching about 2.2 mm in length (holotype 2.15 mm). OH:OT = 2.2–2.6, decreasing with size. Anterior rim nearly vertical with only minor indentation above level of ostial tip. Preventral angle nearly orthogonal, predorsal angle distinct, positioned high on anterior rim. Ventral rim nearly straight to slightly bent. Dorsal rim with broad concavity across entire predorsal section followed by narrow postdorsal angle positioned above cauda and in turn followed by shorter concavity or flat, inclined section toward distinctly expanded postdorsal projection with rounded tip and not bent outward. Posterior rim below postdorsal projection nearly vertical, with orthogonal postventral angle. All rims smooth.

Inner face slightly convex, nearly flat, with narrow, somewhat deepened, centrally positioned, distinctly inclined sulcus. SuL:SuH = 2.5–2.9. Sulcus with very low ostial lobe and rounded anterior and posterior tips, inclined at 10–18°. Subcaudal iugum small, often indistinct or indiscernible after even slight erosion ( Fig. 4c, d ), positioned below sulcus indentation marking ostial–caudal joint. Ventral furrow broad, deep, distinct, reaching from anterior to posterior tips of sulcus, more regularly curved than ventral rim of otolith. Ventral field between ventral furrow and sulcus slightly bulged. Dorsal field with long, narrow dorsal depression, ventrally marked by distinct crista superior toward sulcus and dorsally open to dorsal rim of otolith. Outer face convex, distinctly more convex than inner face and very regularly shaped, smooth.

Discussion Gobius bratishkoi is easily recognized by its characteristic dorsal rim with the two concavities, the nearly vertical anterior rim, and the distinct postdorsal projection with rounded tip that is not bent outward. Further distinguishing characteristics include the outer face being more convex than the inner face and the very low ostial lobe of the sulcus. Gobius bratishkoi resembles the coeval G. mustus Schwarzhans, 2014 but clearly differs in shape of the dorsal rim, the near vertical anterior rim, the postdorsal projection, the strongly reduced ostial lobe, and the very small subcaudal iugum. However, G. bratishkoi , G. mustus , and G. ukrainicus n. sp. described below represent a distinct species group, which cannot be linked to any extant Gobius species and which we term the Gobius mustus complex. Among extant Gobius otoliths, G. auratus Risso, 1810 , G. fallax Sarato, 1889 , and G. vittatus Vinciguerra, 1883 (see Gut et al., 2020; Schwarzhans et al., 2020a for figures) share the closest resemblance in terms of their compressed shapes, their inner faces being nearly flat, and their outer faces more convex. However, the degree of thickness of the outer face and the small size of the sulcus distinguish the Gobius mustus complex from those extant species and indicate that it may represent an extinct clade that is possibly separate from the genus Gobius .

Figures

Fig. 4 Otoliths of Gobius spp.: a–e Gobius bratishkoi n. sp., a holotype, NMNHU-P PI 2555, Kozatskyi Yar, b–e paratypes, b (reversed) Mlyntsi, NMNHU-P PI 2556,c–e (reversed) Kozatskyi Yar, NMB P1211. f Gobius reichenbacherae Schwarzhans,2014, Shydlivshchyna, NMNHU-P PI 2557 (reversed).g–k Gobius ukrainicus n. sp., j holotype, Shydlivshchyna, NMNHU-P PI 2558, g–i, k paratypes, g, i, k NMNHU-P PI 2560, h (reversed) Mlyntsi, NMNHU-P PI 2559